The invention addresses the problem of bonding to a ceramic package surface certain types of temperature-sensitive semiconductor devices at the lowest possible temperature with a silver/glass mixture usually in the form of a dotting paste.
In addition to the well-known gold/silicon eutectic alloy die-bonding process, the advent of glass/ silver is a solution to the eutectic bond stress problems associated with very large silicon die. Silver-loaded glass die-attach materials have demonstrated production reliability on die exceeding 0.4 inch on a side and can be used on both bare silicon and gold-covered silicon. During firing the glass flows to the device and forms a conventional chemical bond, the glass and silver interpenetrate and form a mechanical bond. After completion of the thermal treatment, the microstructure consists of an interlaced network of silver in a sintered glass matrix. The malleability of silver permits greater stress relief in the bond compared with gold eutectic preforms. The process has a wide processing window, and the glass die bonding material offers a significant cost advantage over the Au-Si system.
One major drawback remains the processing temperature which lies in the 400.degree.-500.degree. C. range in an oxidizing atmosphere for several minutes. This tends to create reliability problems to both multi-pin ceramic packages and temperature-sensitive VLSI devices. Lead borate-based glasses do not allow a processing temperature below 400.degree. C. Reduction of the glass processing temperature to about 300-350.degree. C. by a glass formulation change would aid in coping with the processing reliability problems associated with multi-pin ceramic packages and the new generation of silicon integrated devices.
This glass formulation must be totally free of any alkali or halide.